Shielded aircraft spark plug



Och 1941- H. RABEZZANA ET AL 2,258,810

SHIELDED AIRCRAFT SPARK PLUG Filed Jan. 5, 1940 Snnenfors 920202Waszzazza 4' I ttomegs Patented Oct. 14, 1941 I 2,258,810 SHIELDEDAIRCRAFT SPARK PLUG Hector Rabezzana and Alexander J. Battey, Flint,

Mich., assignors to General Motors Corporation, Detroit, Mich., acorporation of-Delaware Application January 5, 1940, Serial No. 312,476

2 Claims.

Our invention relates to spark plugs designed to ignite the combustiblemixture supplied to and burned within the working cylinder of aninternal combustion engine, and particularly to spark plugs for use inshielded ignition systems wherein the conductor or lead wire throughwhich current is supplied to the insulated electrode of the plug isenclosed in a metallic envelope which, in'

turn, is connected to the metallic shell or casing of the plug. The plugitself or, more strictly speaking, the casing thereof being screwed intoa threaded opening in an engine cylinder, it follows that the envelopeenclosing the supply lead is grounded to the engine structure throughthe metallic shell or casing of the plug; thus prevent-' ing the hightension oscillating current in the supply lead from interfering with theoperation of radio receiving apparatus located adjacent the engineequipped with an ignition system having -overheating, than has been thecase in spark plugs such as'have heretofore been used. To that end ourinvention consists in providing the usual shell or casing of the plugwith an upwardly extending shield portion designed to be electricallyconnected with the metallic envelope enclosing the supplylead, incertain relationships between the shield'portion and the centralinsulated elec-- trode of the plug,. and various other featureshereinafter described and claimed.

Our invention includes a tubular lining member of plastic insulatingmaterial molded in place within the upwardly extending shield portion ofthe shell or casing of the plug, and in intimate contact withtheinterior thereof and with the exterior .of the upper portion of theinsulating member of the plug, whereby a better heat conducting path andone of minimum resistance to the flow of heat fromv the centralelectrode and insulating member to the shell or casing, is secured.

In the drawing accompanying and forming a part of this specification:

Figure l is a view showing our improved spark v plug partly inelevation, and partly in section upon avertical central plane; the plugbeing shown about full size.

Figure 2 is a view similar to Figure 1 showing a supply cable secured tothe plug so as to supply current thereto, and the metallic sheath ofwhich 'cable is grounded to the shell or casing of the plug.

Figure 3 is a view illustrating one step of the method whereby a tubularlining member is molded in place within the shell or casing of the plug,.the plug being shown about twice the size it is shown in Figures 1 and2.

Figure 4 is a view similar to Figure 3 but showing a later step of themethod whereby the tubular lining member of our spark plug is molded inplace within the exterior shell or casing thereof.

Referring now to the drawing, the tubular metallic shell or casing ofour improved spark plug is threaded at its lower end 5 to screw into athreaded opening in an engine cylinder and comprises a lower portion 6within which the enlarged central portion of the insulating member 1 ofthe plug is secured, and an upper tubular shield portion 8 shown asintegral with the lower portion, but which may be separate therefrom andsecured to the lower portion in any way so as to form a unitary shell orcasing for the plug.

The insulating member is supported by an internal ledge 9 within thelower portion of the shell, and the upper end' thereof extends into theupper shield portion of the shell and is smaller in diameter than saidshield portion, so as to provide an annular space between the two. Theinsulating member'is held in place within the lower portion 8 of theshell or casing by an externally threaded annular sleeve [0 inengagement with an internally threaded seat within the shield portion 8,as shown, and through which sleeve the upper end of said insulatingmember -vext-ends; an annular holding member being interposed betweenthe sleeve and an annular shoulder ll upon the insulating member. Thisholding member is shown as in the form of a C-shaped gasket I2 made ofspring steel so'that when the sleeve I0 is screweddownward theinsulating member is forced against the ledge 9 t by pressuretransmitted through the gasket [2 and shoulder H; the insulating memberbeing thus permanently held in place within the lower portion 6 of theshell within which it is housed independently of the tubular liningmember to be next described.

After the insulating member 1 has been assembled within the shell orcasing and secured in place therein by the annular sleeve l0 and C-shaped gasket I2, as hereinbefore' explained, a

tubular lining member l3 of plastic material is molded in place withinthe upwardly extending shieldportion 8 of the shell; said member beingmolded in place under pressure so that intimate contact is securedbetween the periphery thereof and 'the interior of the shield portion 8,and between said lining member and the exterior of the upwardlyextending portion of the insulating member. A portion of the material ofthe lining extends over the upper end of the insulating .iember and intocontact with the upper end of .he insulated electrode M as indicated bythe ziumeral l5. The intimate contactsthus secured provide a heatconducting path of minimum resistance to heat flow from the centralelectrode 54 and the upper portion of the insulating member to and intothe lining member i3, and from said member to the shield portion 8 ofthe shell; from which the heat is dissipated into the surroundingatmosphere and a plug which operates at a lower temperature thanheretofore is secured.

The numeral l6 designates a metallic voltage dispersing member,preferably cup-shaped in form as shown, in contact with the upper end ofthe central electrode of the plug and the periphery of which is embeddedin the inner surface of th tubular lining member 53; the purpose of thismember being to distribute the voltage present at the upper end of saidelectrode through an area equal to the circumference of said membertimes its height. The voltage at said upper end being thus dispersed (asdistinguished from being concentrated at one .or more points of limitedarea), it follows that the wall of the lining member 83 is less likelyto be injured, 'as' by a short circuit betweenthe upper end of thecentral electrode and the grounded shell portion a,

or otherwise, than is the case when such voltage is or may beconcentrated at points of limited area upon the inner surface of saidlining member.

In making a spark plug in accordance with our invention theinsulating'member l and central electrode are assembled within the shellor casing and secured in place by the annular sleeve l6 and holdingmember I 2, as hereinbefore appears, and plastic material to form thetubular linin member i3 is put into theupper shield portion 8 of theshell, as indicated by the numeral ii in Figure 3. The plug isthenplaced upon asuitable annular anvil i8 and held in contacttherewithby an annular holding member iii, the two being maintained inalignment by a die block 20; and a.plunger 2| which .is guided byholding member is as shown is forced into the shield part 3 thusdisplacing the plastic material ll and causing it to fill the shieldportion of the shell or casing, as shown in Figure 4; with the resultthat intimate contact is secured between said plastic material and theinterior of the shell,

and with the exterior of the upwardly extending part-of the insulatingmember. A cup-shaped member 22 is put upon the extremity of the plunger2!, see Figure 3, before it is forced into the shield part 8;,and thebottom wall of this joint between the central electrode and the voltagedispersing member 56, which member becomes embedded in the inner surfaceof the tubular lining member at the end of the downward movement of theplunger and is left in place, see Figure 1, as the plunger is withdrawnafter the completion of the molding operation.

The tubular lining member 53 preferably made of Bakelite in which casethe plastic material I! placed in the shield portion 8 of the shellconsists of a suitable amorphous and uncured material or compositionfrom which a finished Bakelite article (the tubular lining memberherein) may be formed; and the plunger 2! is depressed to accomplishmoldingof the member 13 in situ, the same as heretofore explained.Thematerial used is commonly heated to a temperature of around 100 to150 degrees centigrade before being supplied to the plug casing, and theplug with the lining molded in place is commonly kept at a temperatureof around 150 degrees centigrade for around one minute after the moldingoperation to permit the Bakelite material to coalesce and form anintegral and solid lining member.

Having" thus described and explained our invention, we claim and desireto secure by Letters Patent:

1. A spark plug comprising a hollow metallic shell or casing threaded atits lower end to screw into an opening an engine cylinder and having alower portion for housing an insulating member, and having also an uppershield portion; an insulating member located within the lower andextending into the upper shield portion of said shell, and the upper endof which insulating member is smaller in diameter than the interior ofsaid shield portion so as to provide an annular space between the two;means for securing said insulating member in place within the lowerportion of -said shell; and a tubular lining member of plastic materialmolded in place within said annular space and in intimate contact withthe interior of said shield portion and with the exterior of the upperend of said insulating member, and which lining extend above the upperend of said insulating member.

2; In a spark plug of the class described, a hollow metallic shell orcasing threaded at its lower end to screw into an opening in an enginecylinder and having an internal supporting ledge, an internally'threadedseat, and a shield portion extending above said seat; an insulatingmember within said .shell and supported by said ledge,

and which member extends above said threaded seat and into said shieldportion and has an annular shoulder; an externally threaded annularsleeve in engagement with said threaded-seat and through which the upperend of said insulating member extends; an annular holding member betweensaid sleeve and the shoulder aforesaid of said insulating member; and atubular lining member of plastic material molded in place within saidshell and in intimate contact with the interior of the shield portionthereof and with the exterior of th upwardly extending portion of saidinsulating member.

HECTOR. RABEZZANA.

ALEXANDER J. BA'I'I'EY.

